“None” actually runs grayscale by varying the power of the laser to darken/lighten as needed. It’s very finnicky and has to be dialed in painstakingly for each material, but you can get some wonderful results. Such as this;
I did an explanation between dithering vs grayscale feature in Luban in this thread if you want some information on it:
As far as the actual dithering algorithm options available, they’re mostly how it mathematically determines the dithering and is mostly up to personal preference. A good rule of thumb is Stucki gives the best details for real life images, with minimal artifacts. Atkinson however, is high contrast, this is good for smooth/solid colours, like drawings or non-real life images. Say, logos, webcomics, etc. You won’t really see much of a difference in the preview, but you will in the finished result.
The grayscale conversion is how it converts to grayscale before dithering, that’s a bit more on photo editing that is outside of my scope. I assume it has to do with brightness values vs colours, etc.